1. Field of the Invention
The present invention relates to an electric-component mounting system arranged to mount electric components (including electronic components) on a circuit substrate, and a process of fabricating a printed-circuit board, which includes a step of mounting the electric components on the circuit substrate.
2. Discussion of Related Art
An electric-component mounting system is arranged to mount electric components on a circuit substrate which is held at a predetermined component-mounting position. A typical type of such an electric-component mounting system widely used in the art includes (A) a substrate-holding device arranged to hold the circuit substrate on which the electric components are to be mounted, (B) a mounting unit provided with a mounting head operable to receive and hold a selected electric component in a predetermined component-supplying area, and mount the electric component onto the component-mounting surface of the circuit substrate in a predetermined component-mounting area, and (C) a mounting-unit moving device operable to move the mounting unit in a plane parallel to the circuit substrate, between an appropriate component-supplying position in the component-supplying area and an appropriate component-mounting position in the component-mounting area.
A representative example of the mounting-unit moving device used in the electric-component mounting system of the type indicated above uses a so-called “XY slide assembly type” (XY robot type) including an X-axis slide and a Y-axis slide. This XY slide assembly type mounting-unit moving device generally includes (A) a relatively long X-axis slide, (B) an X-axis-slide moving device operable to move the X-axis slide in an X-axis direction perpendicular to its longitudinal direction and parallel to the surface of the circuit substrate, (C) a Y-axis slide slidably mounted on the X-axis slide, and (D) a Y-axis-slide moving device operable to move the Y-axis slide on the X-axis slide in a Y-axis direction perpendicular to the X-axis direction and parallel to the longitudinal direction of the X-axis slide. The mounting unit is mounted on the Y-axis slide, so that the mounting unit is movable in the X-axis and Y-axis directions in the plane parallel to the circuit substrate. Usually, a printed-circuit board is fabricated by mounting a multiplicity of electric components of various kinds on the circuit substrate. To fabricate the printed-circuit board, therefore, the mounting-unit moving device of the XY slide assembly type is required to be reciprocated a large number of times between the component-supplying area and the component-mounting area. In this respect, the electric-component mounting system using the mounting-unit moving device of the XY slide assembly type generally suffers from a comparatively low degree of efficiency in fabricating the printed-circuit board.
To improve the efficiency of mounting the electric components on the circuit substrate in the electric-component mounting system of the XY slide assembly type discussed above, it is considered to use a mounting device of twin-unit type (twin head type) which includes two mounting units. For instance, the mounting device of the twin-unit type may include two X-axis slides movable on the same guide rails, and two Y-axis slides which are slidably mounted on the respective two X-axis slides and on which the respective two mounting units are mounted. In this case, two component-supplying devices are provided on the respective opposite sides of the circuit substrate, and the mounting head is arranged such that the mounting unit mounted on the Y-axis slide on one of the two X-axis slides is assigned to receive the electric components from one of the two component-supplying devices, and the mounting head mounted on the Y-axis slide on the other X-axis slide is assigned to receive the electric components from the other component-supplying device, so that the two mounting units alternately operate to mount the electric components on the circuit substrate. Namely, one of the two mounting units receives the electric component from one of the two component-supplying devices, while at the same time the other mounting unit mounts the electric component on the circuit substrate in the component-mounting area.
In the electric-component mounting system using the mounting device of the twin-unit type having two mounting units that are moved in a plane between the component-supplying area and the component-mounting area, however, a need of avoiding a mutual interference of the two mounting units makes it difficult for the two mounting units to stay in the component-mounting area at the same time, and requires the two mounting units to be moved relative to each other in a suitably timed relation with each other. Accordingly, either one of the two mounting units is often required to be held stationary until a risk of the interference with the other mounting unit is eliminated. In this respect, a considerable improvement in the component-mounting efficiency is not expected. In addition, the provision of the two component-supplying devices on the opposite sides of the component-mounting area (circuit substrate) undesirably increases the overall size of the electric-component mounting system including the component-supplying devices, and the required space for installation of the system, leading to deteriorated efficiency of space utilization on the side of the user.
To improve the efficiency of mounting the electric components on the circuit substrate in the electric-component mounting system of the XY slide assembly type discussed above, it is also considered to use a mounting device which includes a plurality of mounting units, which are mounted on respective Y-axis slides slidably mounted on a single X-axis slide, for example. In the electric-component mounting system of this type, the mounting units can be moved independently of each other, so that the required number of times of reciprocation of the mounting units between the component-supplying and component-mounting areas can be reduced, and the component-mounting efficiency can be improved to some extent.
However, the component-mounting spots on which the electric components are to be mounted on the circuit substrate are not necessarily spaced from each other in the Y-axis direction parallel to the longitudinal direction of the X-axis slide. In the electric-component mounting system of the type described just above, therefore, it is difficult to perform component-mounting operations such that a plurality of electric components are simultaneously mounted on the respective component-mounting spots on the circuit substrate, by the respective two or more mounting units which are mounted on the respective Y-axis slides carried by the single X-axis slide. That is, a component-mounting operation by each mounting unit cannot be initiated after the completion of a component-mounting operation by the other mounting unit, until the X-axis slide is moved to a position corresponding to the component-mounting spot at which the electric component is to be mounted by the above-indicated each mounting unit. Thus, there is a limitation in the improvement in the component-mounting efficiency in the electric-component mounting system of the type using a plurality of mounting units on a single X-axis slide.